However, running the same command on Windows 7 gives a faithful jpeg image - the third attachment.

I used the 64 bit JRE 8 update 131 In both the Windows and Linux environments.

I used to suffer from lots of PDF->Image conversions giving garbled text at PDFBox1.8. Upgrading to PDFBox2.0 has fixed most of these issues, except for this odd one with identity-H encoding with the Linux JRE.